(1) Field of the Invention
This invention relates to buoys.
(2) Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98.
Buoys are used for mooring purposes and as navigational marks. The invention will be explained in relation to catenary anchor leg mooring buoys but, it will be appreciated, may be applicable to buoys of other types. Conventional catenary anchor leg mooring (CALM) buoys are used extensively to facilitate offshore marine terminals for the import or report of crude oil (and other fluids).
A CALM buoy is generally moored to a 4, 6 or 8 point mooring system (dependent upon operational requirements, environmental conditions, water depth etc). The tanker to be loaded (or offloaded) moors directly to the buoy and connects to a floating hose which carries the fluid product.
The fluid hose and the mooring assembly arrangements on a CALM buoy are swivel mounted in order that the tanker can “weathervane” around the buoy thus maintaining a heading into the wind/weather at all times.
The use of CALM buoy provides a low cost marine terminal as dedicated port or harbour facilities are not required for tanker mooring. The CALM buoy design allows the tanker to moor directly to the buoy and a fluid transfer pipeline may run from a shore facility to the CALM buoy.
Conventional CALM buoys have been in use in the offshore industry for many years and have proved to be a cost efficient method for the transfer of petroleum products from a seabed production facility to an off take tanker (or vice versa).
Conventional CALM buoys generally take the form of a large steel cylinder with a central opening or so-called “moonpool” and a rotating turntable or arm section fitted to the top of the buoy. Generally the turntable is made up of three “arms”, the mooring arm, the off take arm and a counterbalance arm.
The tanker is moored to the mooring arm of the turntable via a hawser mooring system. The tanker is free to weathervane around the buoy by the mooring loads applying rotational forces to the turntable. The turntable is fitted to the main body of the buoy via a large slew bearing arrangement.
A riser/hose system is connected from the seabed facility to a fluid swivel located in the centre of the moonpool. The output flange of the fluid swivel is connected to a pipe that is fixed onto the turntable's off take arm and leads off the buoy to an off take hose connected to the tanker.
The main body of the buoy is generally moored to the seabed via four, six or eight mooring lines. The method used to tension and attach the mooring lines to the buoy differs between designs, but generally the lines are tensioned with an onboard winch and gantry arrangement also used for attaching the mooring hawser and off take hoses. The mooring lines are then locked into place by a locking device such as a chain stopper. The components of the mooring system are dependent on the water depth, the environment associated with the location where the buoy is to be moored, and the size of the off take tanker.
Conventional CALM buoys generally have a hull constructed of steel plate by traditional ship building techniques requiring plate benders. Webs, beams and girders are welded inside the hull which is divided into several tanks. The buoy has a central moonpool and a steel turntable. Bending plate, in effect, doubles its cost.